Strip Tags thats are NOT in [code] [/code] segment

Question

I'm trying to find a way to strip tags from a user-inputted string except from tags that are wrapped in the [code] [/code] BB style tag.

For example, a user may enter this:

<script>alert("hacked");</script>
[code]<script>alert("hello");</script>[/code]

What I would like is the "hacked" alert to be removed, but not the "Hello" alert.

I would like to remove ALL tags (php, html, css, js) outside of the [code] but allow anything within them.

So far, I've got the following code to do the reverse of what I would like:

preg_replace('/\[code\](.*?)\[\/code\]/ise','strip_tags(\'$1\')',$code)

Answer 1

This is where regular expressions are not ideal. Regular expressions are superb when you know "what you want" but not "what you don't want". My suggestion is that you try to find an alternative way of doing the same thing, but without regular expressions.

Answer 2

You want to use an HTML Parser for this job.

I don't know PHP but Google found this HTML Parser for PHP.

Answer 3

Use a simple parser like this:

stack-pointer = 0
while not finished:
    stack-pointer-n = code-start-matched or endl
    tag-free-str = regex-magic-to-strip-tags(extract-str(stack-pointer, stack-pointer-n))
    preserve-str = extract-str(stack-pointer-n, code-endl-matched or endl)
    stack-pointer = code-endl-matched + 1
    push(tag-free-str)
    push(preserve-str)

Answer 4

I'm not sure if this is the best algorithm, but here's an idea.

1. Remove all the [code] blocks into an array
2. Strip tags from the remaining string
3. Re-insert the previously removed [code] blocks.
4. Voila!

Here's a stab at that algo

<?php

header( 'Content-Type: text/plain' );

$input = <<<BB
[code]<script>alert("hello");</script>[/code]
some text <script>alert("hacked");</script> some other text
[code]<script>alert("hello");</script>[/code]
some text <script>alert("hacked");</script> some other text
[code]<script>alert("hello");</script>[/code]
BB;

echo strip_custom( $input );

function strip_custom( $content )
{
  $pattern = "#\\[code].*?\\[/code]#i";

  if ( preg_match_all( $pattern, $content, $codeBlocks ) )
  {
    return array_join( $codeBlocks[0], array_map( 'strip_tags', preg_split( $pattern, $content ) ) );
  }
  return strip_tags( $content );
}

function array_join( array $glue, array $pieces )
{
  $glue       = array_values( $glue );
  $pieces     = array_values( $pieces );
  $piecesSize = count( $pieces );

  if ( count( $glue ) + 1 != $piecesSize )
  {
    return false;
  }

  $joined = array();
  for ( $i = 0; $i < $piecesSize; $i++ )
  {
    $joined[] = $pieces[$i];
    if ( isset( $glue[$i] ) )
    {
      $joined[] = $glue[$i];
    }
  }
  return implode( '', $joined );
}